The present invention relates to time synchronization, and, more particularly, to a system and method for synchronizing the time of clocks and devices with clock functions using a telephone.
Computing devices are not limited to personal computers, and often are found in everyday appliances and tools, such as automobiles, microwave ovens, cellular phones, televisions, video cassette recorders (VCRs), audio/stereo systems, home alarm systems, etc. Timekeeping devices including digital clocks are a pervasive feature of our computerized society; for, many computing devices utilize a clock circuit or a timer during operation, for example, to activate at a predetermined point in time to operate an alarm or to control other devices, such as video recording devices.
Although the traditional term "clock" often refers to a timekeeping device with the sole function to maintain and display the time, many everyday devices often serve multiple functions, including maintaining and displaying the time, and so perform also as clocks. In particular, such devices may operate using electricity, and typically include electronics such as solid-state components and oscillators for maintaining the time. Accordingly, as defined herein, the term "clock" includes any devices having an electrically-powered timekeeping component.
With so many clocks available and presented to persons or organizations in everyday life, synchronization between multiple clocks is often required. For example, seasonal clock adjustments such as for Daylight Savings Time may be a daunting task in view of the multiple clocks within a home. Other problems affecting multiple clocks may be technical in nature. For example, losses of power to the oscillators for a significant period of time with limited or no power backup disrupt the timekeeping functions of the clocks. Further, many clocks may operate off of a common power source such as the electrical power to a house, and so a common loss of power often affects multiple clocks at once.
In addition, electronic clocks using oscillator crystals occasionally need to be reset due to accumulated drift during normal operation. Further, with constant timekeeping operation, clocks may also experience local oscillator aging effects, which in turn cause accumulated drift and reduce the accuracy of such clocks.
Accordingly, a need exists to counter the disruptive effects on the timekeeping functions of electronic clocks. In addition, a need exists to reset multiple clocks and timekeeping devices with greater efficiency.
In the prior art, clocks and other timekeeping devices are commercially available which automatically set themselves in response to received time transmissions. For example, clocks are available which are automatically set in response to the shortwave time transmissions from the WWV radio station of the National Institute of Standards and Technology (NIST). However, such clocks are not only costly for the average consumer but also such clocks would not be placed in abundance in household appliances or automobiles.
Another solution to automatically adjust clocks involves using portable Global Positioning System (GPS) receivers. However, the cost for such GPS receivers is still generally prohibitive for consumers, and such GPS receivers require an antenna with a clear view of the sky for satellite tracking, and so the use of such GPS receivers for clock synchronization is not practical in the case of multiple household clocks.
Accordingly, a need exists for a relatively inexpensive household or portable device which may operate with other devices with clocks to synchronize such clocks.
In the prior art, a line of VCRs produced by the "SONY" Corporation includes a time setting system, in which each VCR sets the clock therein in response to time codes carried within the vertical blanking intervals of conventional TV signals. However, such a clock setting solution may be relatively expensive to implement in multiple household appliances since each appliance would require a tuner or other TV signal decoding circuitry to read the time codes from the vertical blanking intervals, and each appliance would have to be able to receive such TV signals, for example, through bulky coaxial cables.
Thus, there is a need for a relatively simple and inexpensive system which communicates with multiple appliances to set the clocks therein.
Also, U.S. Pat. No. 5,600,711 to Yuen discloses a system for setting the time on remote appliances, which requires a telephone connection to the remote appliance and a time setting device, and with a predetermined command sequence including a time value to be sent to address and set each remote appliance. Each remote appliance thus addressed receives and adopts the time value sent over the telephone lines. In another system described in U.S. Pat. No. 5,805,530 to Youngberg, a master clock device, which is not a telephone, transmits time information in time codes as well as accuracy information via infrared or radio frequency (RF) waves. However, implementation of such command sequences and communication protocols for sending and receiving such command sequences, time codes, time values, and accuracy information increases the complexity of the components.
A need exists for a relatively simple system for synchronizing the time of a plurality of appliances without the complexity of transmitting and receiving command sequences and accuracy information to the appliances.